netdev - Re: [PATCH bpf 2/4] xsk: frame could be completed more than once in SKB path

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Date:   Wed, 27 Jun 2018 11:19:50 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Magnus Karlsson <magnus.karlsson@...el.com>
Cc:     bjorn.topel@...el.com, ast@...com,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>, qi.z.zhang@...el.com,
        pavel@...tnetmon.com
Subject: Re: [PATCH bpf 2/4] xsk: frame could be completed more than once in
 SKB path

On Wed, Jun 27, 2018 at 7:02 AM, Magnus Karlsson
<magnus.karlsson@...el.com> wrote:
> Fixed a bug in which a frame could be completed more than once
> when an error was returned from dev_direct_xmit(). The code
> erroneously retried sending the message leading to multiple
> calls to the SKB destructor and therefore multiple completions
> of the same buffer to user space.
>
> The error code in this case has been changed from EAGAIN to EBUSY
> in order to tell user space that the sending of the packet failed
> and the buffer has been return to user space through the completion
> queue.
>
> Fixes: 35fcde7f8deb ("xsk: support for Tx")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> Reported-by: Pavel Odintsov <pavel@...tnetmon.com>

Acked-by: Song Liu <songliubraving@...com>


> ---
>  net/xdp/xsk.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 3b3410ada097..d482f727f4c2 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -268,15 +268,15 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
>                 skb->destructor = xsk_destruct_skb;
>
>                 err = dev_direct_xmit(skb, xs->queue_id);
> +               xskq_discard_desc(xs->tx);
>                 /* Ignore NET_XMIT_CN as packet might have been sent */
>                 if (err == NET_XMIT_DROP || err == NETDEV_TX_BUSY) {
> -                       err = -EAGAIN;
> -                       /* SKB consumed by dev_direct_xmit() */
> +                       /* SKB completed but not sent */
> +                       err = -EBUSY;
>                         goto out;
>                 }
>
>                 sent_frame = true;
> -               xskq_discard_desc(xs->tx);
>         }
>
>  out:
> --
> 2.7.4
>